A senior Republican congressman has bowed to intense political pressure and apologised for comments in which he referred to Hispanic immigrants as "wetbacks"

Don Young, who has represented the entire state of Alaska in the House of Representatives since 1973, said in a statement that there was "no malice in my heart or intent to offend" but he was "sorry" over a "poor choice of words". His words came after an initial attempt to limit any backlash over his use of the racial slur without issuing a frank apology was attacked by colleagues in the House, including Republican leader John Boehner.

The House speaker said Friday that the remark – which was made by Young during a radio interview – was "offensive and beneath the dignity of the office holds". "I don't care why he said it; there's no excuse and it warrants an immediate apology," Boehner added, in a strongly worded admonishment.

The Democrat minority leader, Nancy Pelosi, attacked Young over his "deeply offensive" remark.

In a statement released on Thursday, Young said he had used the term innocently, and had meant no harm by it. Young, 79, said the phrase was one he "commonly used during my days growing up on a farm in central California". But his words fell short of a full apology. Later on Friday he issued a broader statement.

"I apologise for the insensitive term I used during an interview in Ketchikan, Alaska," Young said. "There was no malice in my heart or intent to offend; it was a poor choice of words. That word, and the negative attitudes that come with it, should be left in the 20th century, and I'm sorry that this has shifted our focus away from comprehensive immigration reform."

The debate over comments by Young – an often controversial figure who is being investigated by the House's ethics committee over gifts and the use of campaign funds – has come at a sensitive time for Republicans, with many in the party looking to soften its line on immigration following November's election defeat. A record number of Hispanics voted, making up 10% of the overall electorate, according to the Pew Research Center. Of those, 71% favoured Barack Obama over his Republican rival, Mitt Romney.

American Crossroads – the conservative Super Pac backed by former George W Bush adviser Karl Rove – recently launched a fighting fund to counter "undisciplined" primary candidates from the fringe of the party. In November, Republicans in a number of high-profile congressional seats faced a backlash over comments on rape and abortion.

Meanwhile, a Michigan member of the Republican National Committee (RNC) was under increasing pressure on Friday to resign over an anti-gay diatribe posted on Facebook.

Dave Agema, who served as a state congressman from 2007 until late last year, put up an excerpt of an article titled Everyone Should Know These Statistics On Homosexuals. Among other homophobic slurs, the article describes homosexuality as a "filthy lifestyle", adding that gay and lesbian people have an agenda of turning people against Christianity. It also claims that many gay people admit to being paedophiles.

A group of 21 Michigan Republicans have since called the paper "deplorable". Agema also appeared to receive a rebuke from RNC chairman Reince Priebus. Priebus said that although the party's position on gay marriage – an issue that this week went before the supreme court – is clear, "all human beings deserve to be treated with dignity and respect".

Despite increasing pressure over the article posted on his Facebook page, Agema told the Associated Press that he would "absolutely not" resign from the RNC.